BUILDING ELEMENT OR RETAINING ELEMENT THAT IS USABLE FOR THE PLASMA PROCESSING OF WORKPIECES AND METHOD FOR PRODUCING A MECHANICAL CONNECTION BETWEEN A BUILDING ELEMENT AND A RETAINING ELEMENT

Description

[0001] The invention relates to a component or holding element that can be used for the plasma processing of workpieces, as well as a method for its production. Such components or holding elements can be used in particular in tungsten inert gas welding (TIG), plasma welding, or plasma cutting. They can preferably be components of a plasma torch.

[0002] A mechanical connection between a component and a holding element can be established by positive and / or non-positive locking, for example in the form of a screw connection or a press fit. In each case, the areas of a respective component and holding element used for a mechanical connection are designed to be complementary to one another. For example, an internal or external thread is formed in these areas, with which a positive and non-positive connection can be established between the component and holding element. In a press fit, a recess (in particular a bore) in a holding element and a complementary outer contour with corresponding dimensions, which is formed on a component, can be used for a non-positive connection with suitable respective dimensions.

[0003] When connecting components and their respective holding elements, at least good thermal conductivity is desired. In some cases, electrical conductivity is also required in the connection area. For this purpose, so-called conductive pastes are typically used. These have a pasty consistency and are applied to at least one of the surfaces of a component or holding element in the area used to create the connection. A particular disadvantage here is that precise dosing and locally homogeneous application of a conductive paste is not possible or only very rarely. This leads to conductive paste being released during operation and potentially getting onto the surface of the workpiece being machined or into a plasma jet. This can lead to considerable quality losses.

[0004] On the other hand, this can lead to an inhomogeneous distribution of the applied conductive paste on the respective surface, resulting in very different thermal and possibly even tribological conditions locally, which in turn can lead to local welding, known as "galling." This can make the necessary replacement of a damaged or worn component on a plasma torch particularly problematic, and can even result in damage to the plasma torch, even though only a wearing part, such as an electrode or nozzle, needs to be replaced.

[0005] For example, EP 0 544 386 A1 discloses a coated arrangement and a manufacturing method that can be used for welding torches.

[0006] EP 2 175 149 A2 discloses possibilities for the use of electrically conductive adhesive compositions containing carbon nanotubes.

[0007] DE 10 2016 006 626 A1, which forms the basis for the preamble of the independent claims, relates to multi-component electrodes for a plasma cutting torch.

[0008] DE 10 2009 054 427 A1 discloses a method for applying carbon / tin mixtures to metal or alloy layers.

[0009] It is therefore an object of the invention to provide possibilities for improving the conditions of a mechanical connection between a component and a suitable holding element which are used in thermal plasma processing, and in particular to enable improved and safe thermal and, if appropriate, electrical conductivity in conjunction with safe and simplified interchangeability.

[0010] According to the invention, this object is achieved with an element having the features of claim 1. A method for manufacturing the element is defined in claim 9. Advantageous embodiments and further developments of the invention can be realized with features defined in subordinate claims.

[0011] A component according to the invention is designed to be mechanically connectable to a holding element or a holding element to a component in a complementarily designed region.

[0012] According to the invention, the surface of a component or a holding element in the complementary region is provided exclusively with a coating formed from particles. The particles are electrically and thermally conductive.

[0013] In an example not according to the invention, the coating is formed with a purely organic chemical compound containing fluorine, or the coating is formed with a polyamide. In this example, a layer formed with depressions, perforations, or elevations, formed from one of these organic compounds, forms the coating. A coating formed from an appropriate organic material can achieve sufficient temperature resistance and tribological properties that can at least prevent the aforementioned "galling."

[0014] If the coating is formed solely with particles, these properties can also be adequately achieved. Even improved thermal and electrical conductivity can be achieved in the connection area. With a mechanical threaded connection, this mechanical connection can be easily removed even after extended use in a plasma torch. The disadvantages of the conductive pastes used in the prior art are avoided.

[0015] The coating can be formed on one of the two complementary surfaces in the connecting region with graphite particles, carbon nanotubes, particles of a metal sulfide or a metal nitride, in particular boron nitride or aluminum nitride. According to the invention, the particles should be

[0016] are held to the surface by adhesive forces without the need for an organic or inorganic binder.

[0017] According to the invention, the particles, in particular graphite particles, have a maximum average particle size d 50 of 50 µm, preferably in the range of a maximum of 35 µm to a minimum of 4 µm. If carbon nanotubes are used as particles for forming a coating, they can be used in the commonly commercially available sizes.

[0018] As already mentioned, the complementary areas of the component and retaining element used for mechanical connection should have a thread that allows the component and retaining element to be connected in a form-fitting and friction-locking manner. This thread can advantageously be a thread with a reduced pitch compared to a standard thread (fine thread).

[0019] A component or holding element can be selected from an electrode, an electrode holder, a nozzle, a protective cap, a nozzle holder, and a protective cap holder. For example, an electrode represents a component and an electrode holder represents a holding element. A nozzle can be a holding element for a nozzle protective cap. The component or holding element can also be an electrode holder provided with an emission insert. The emission insert is inserted into the electrode holder with a press fit or a screw connection, wherein the emission insert is preferably made of tungsten, hafnium, zirconium, or an alloy of one of these metals, and the electrode holder is made of copper, silver, or an alloy of one of these metals.Preferably, the electrode holder may have an outer jacket region that can be exchangeably connected to a complementary region of an electrode holder or a torch shaft. One of the surfaces of these regions may be provided with a coating to avoid the disadvantages of the prior art, particularly when replacement is required. An electrode holder may be made of copper, silver, or an alloy of one of these metals.

[0020] An electrode formed with an electrode holder and an emission insert can be designed as a pointed or flat electrode.

[0021] A component or holding element that can be used in the invention can be part of a burner that can be cooled by means of a fluid.

[0022] A respective component or holding element may preferably be a wearing part which can be replaced more easily if necessary, but whose properties during operation are not or only insignificantly impaired compared to the state of the art.

[0023] Advantageously, a component or holding element can be made of copper, silver, zinc or an alloy of these chemical elements.

[0024] During production, at least one surface of the complementary region of a component or holding element is coated with the particles or with a suspension containing the particles before establishing a mechanical connection between the respective component and holding element. However, in the example not according to the invention, an organic layer made of a fluorine-containing polymer or a polyamide can also be formed before establishing a mechanical connection between the respective component and holding element.

[0025] In this example, which does not correspond to the invention, depressions or elevations can be formed within the complementary region when forming a layer of organic material, for example by means of a mask or corresponding surface treatment of the surface. It is also possible to apply a release agent locally to the surface, subsequently apply the organic material forming the layer, and then remove the release agent again. The release agent can be a sacrificial material that can be removed thermally or with a suitable solvent or selective etching agent. In this way, individual elevations and depressions arranged at a distance from one another can be obtained in a region of the layer or in a complementary connecting region.Advantageously, pure particles can be applied mechanically, preferably by brushing or painting onto the surface to form the coating.

[0026] A suspension can be applied by spraying, brushing, or dip coating. Following this, and according to the invention, drying takes place to remove the liquid components.

[0027] A suspension containing a liquid that gasifies at a maximum temperature of 70 °C, preferably 50 °C, and does not form an acid can be advantageously used. It is most advantageous if the liquid gasifies slightly above normal room or ambient temperature, as this requires no additional or only minimal drying measures.

[0028] Alone or in addition thereto, a suspension can be used in which graphite particles or carbon nanotubes are contained, preferably in a proportion of at least 0.3 mass%, particularly preferably at least 1 mass%.

[0029] If a water-based suspension containing carbon nanotubes is used, it is advantageous to add a surfactant to ensure a homogeneous distribution of the carbon nanotubes in the liquid. In this case, the surfactant should be removed after the suspension has been applied to the respective surface, which can be achieved by washing with a suitable solvent for the surfactant.

[0030] Water, an alcohol, especially isopropanol or ethanol, can be used as the liquid for the suspension. An oil can also be used as the liquid. An oil can also be present in the suspension in a mixture or as a solution with one of the aforementioned liquids. Additionally, at least one protective colloid, at least one preservative, at least one emulsifier, and / or at least one surfactant can be included.

[0031] If particles are present in the suspension, they should have a maximum average particle size of 1 µm.

[0032] With a coating present or formed according to the invention, improved thermal conductivity can be achieved in the region of the mechanical connection between a component and a holding element designed to fix this component, which, in particular when using a threaded connection, can and should be easily and safely released again even after a period of operation, which may be necessary, for example, when a component or holding element needs to be replaced due to wear or damage.

[0033] A coating formed exclusively with graphite particles should advantageously be formed with at least three particle layers arranged one above the other.

[0034] Since the coating also adheres securely and permanently to the respective surface, the disadvantages of previously used conductive pastes do not occur.

[0035] The invention will be explained in more detail below by way of example.

[0036] It shows: Figure 1 a cross-sectional view of a torch for tungsten inert gas welding.

[0037] The Figure 1 The sectional view shown clearly shows that, in such a burner, several elements can be a component or holding element within the meaning of the invention. For example, an emission insert 2.2 is pressed into a bore in an electrode holder 2.1. In this example, the electrode holder 2.1 is made of copper. The emission insert 2.2 is made of tungsten.

[0038] In a region 2.1.1, a thread is formed on an outer surface of the electrode holder 2.1. This region with the thread 2.1.1 is screwed into a complementary thread, in particular a fine thread, which is arranged in a region 4.1 of the electrode holder 4, which is held in the housing 3 of the torch. The electrode holder 2.1 can form a component, and the electrode holder 4 can form a holding element within the meaning of the invention.

[0039] A coating is preferably formed on the surface of the thread 2.1.1, which is formed in the area of ​​the electrode holder 2.1.

[0040] The coating can be applied, as described below, to the surface of the thread 2.1.1 in the area before the electrode holder 2.1 with the emission insert 2.2 fastened therein can be connected in a form-fitting and force-fitting manner by screwing it to the electrode holder 4.

[0041] In the present exemplary embodiment, a suspension is created from powdered graphite and ethanol, with which the thread 2.1.1 is coated by immersion and subsequent air drying. The suspension contained graphite with a solids content in the range of 0.5% to 5% by mass, in particular 2% to 5% by mass.

[0042] In the interior of the housing 3 of the burner there is also a nozzle 10 which is designed as a hollow cylinder at least in the distal region, and the nozzle 10 is dimensioned and arranged such that the electrode holder 2.1 with the emission insert 2.2 and the electrode holder 4 are at least partially arranged in its interior, and a gap is formed for guiding an inert gas out of the burner.

[0043] An external thread 10.1 is formed on an outer surface of the nozzle 10, onto which an internal thread 7.1 of a protective cap 7 can be screwed, thus connecting the nozzle 10 and protective cap 7 to one another in a form-fitting and friction-locking manner. The external thread 10.1, which is formed in a region of the nozzle surface, and the internal thread 7.1, which is formed on the inner wall of the protective cap 7, form complementary regions. Preferably, the surface of the internal thread 7.1 of the protective cap 7 can be provided with a coating, as this can be advantageous in the event of replacement due to wear.

[0044] The coating can be formed as already described for the formation of a coating in the area of ​​the thread 2.1.1.

[0045] The nozzle 10 can therefore represent a holding element and the protective cap 7 a component within the meaning of the invention.

[0046] Of course, other elements of the Figure 1The burner shown can be designed according to the invention and connected to one another. In a form not shown, this can be, for example, the nozzle 10 in a nozzle holder (not shown) in the housing 3.

[0047] In the example shown, the housing 3 also has a supply 8 and a discharge 9 for a cooling medium guided into the housing 3 into a cavity 5 through a cooling pipe 6.

Claims

1. A component or retaining element which are mechanically connectable to one another in a region formed in a complementary manner and are usable for the plasma processing or thermal processing of workpieces with use of an electric arc, characterized in that the surface of the component (2.1, 7) or of the retaining element (4, 10) in the region formed in a complementary manner is provided exclusively with a coating formed with particles, wherein the particles are electrically and thermally conductive and are held on the surface solely by adhesion forces, without the need to use an organic or inorganic binder, and wherein the particles have a d50 mean particle size of 25 µm, preferably at most 20 µm.

2. The component or retaining element according to claim 1, characterized in that the coating is formed with graphite particles, carbon nanotubes, a metal sulfide, a metal nitride, in particular boron nitride or aluminum nitride.

3. The component or retaining element according to any one of the preceding claims, characterized in that the respective component or retaining element (2.1, 7, 4, 10) is an exchangeable part of a tungsten inert gas (TIG) welding torch, a plasma welding torch, a plasma arc torch or a MIG / MAG torch.

4. The component or retaining element according to any one of the preceding claims, characterized in that the particles, in particular graphite particles, have a maximum d50 mean particle size of 25 µm, preferably at most 20 µm.

5. The component or retaining element according to any one of the preceding claims, characterized in that a thread (2.1.1) is provided in the complementary regions of the component (2.1, 7) and retaining element (4, 10) and may be used to connect the component (2.1, 7) and retaining element (4, 10) to one another form-fittingly or in a frictionally engaged manner.

6. The component or retaining element according to any one of the preceding claims, characterized in that a component (2.1, 7) or retaining element (4, 10) is selected from an electrode, an electrode mount, a nozzle (10), a protective cap (7), a nozzle mount and protective cap mount.

7. The component or retaining element according to any one of the preceding claims, characterized in that the component (2.1, 7) or retaining element (4, 10) is formed from copper, silver, zinc or an alloy of these chemical elements.

8. The component or retaining element according to any one of the preceding claims, characterized in that the component (2.1, 7) or retaining element (4, 10) is an electrode socket (2.1), in which an electrode is inserted with a press fit or a screw connection, wherein the electrode is preferably formed from tungsten, hafnium, zirconium or an alloy of one of these metals and the electrode socket is formed from copper, silver or an alloy of one of these metals.

9. A method for producing a mechanical connection between a component and a retaining element according to any one of the preceding claims, characterized in that a surface of the complementary region of the component (2.1, 7) or of the retaining element (4, 10) is coated with the particles or with a suspension containing the particles before a mechanical connection is established between the respective component (2.1, 7) and retaining element (4, 10), wherein a drying operation is performed subsequently to the application of a suspension, during which drying operation the liquid constituents are removed, wherein the particles have a d50 mean particle size of 25 µm, preferably at most 20 µm.

10. The method according to the preceding claim, characterized in that the pure particles are applied mechanically to the surface, preferably by being painted on or brushed on or the suspension is applied by being sprayed on, brushed on or by dip-coating.

11. The method according to any one of the two preceding claims, characterized in that a suspension comprising a liquid that transitions into the gas phase at a temperature of at most 70°C, preferably at most 50°C and that does not form any acid is used, and / or a suspension in which carbon nanotubes with a proportion of at least 0.5 mass % to 5 mass %, preferably at least 1 mass % are contained is used.

12. The method according to any one of the three preceding claims, characterized in that the suspension is produced with water, an alcohol, in particular isopropanol or ethanol and / or an oil.